Mapped instruments and staff styles not pasting properly

I do a lot of work with sampled instruments and take advantage of the facilities of mapped instruments and staff styles. Once I've created them I want to be able use them in other projects. The problem is, they don't paste properly between projects.

When I copy a mapped instrument from one project and paste it to another, all my custom groups are gone and replaced by * New Group. When I copy and paste a staff style, all the group assignments are there, with the correct positions, but the pop up Drum Group menu is empty. Those custom groups are nowhere to be seen in either the staff styles or mapped instruments interfaces.